The present invention relates to bicyclic[3.1.0]amines and to pharmaceutical compositions containing them and to their use in the treatment of central nervous system disorders, cognitive disorders, schizophrenia, dementia and other disorders in mammals, including humans. These compounds exhibit activity as inhibitors of the glycine type-1 transporter.
Schizophrenia, a progressive neurological disease, is manifested in its early stages as thought disorders such as hallucinations, paranoid delusions, and bizarre thought patterns, collectively known as positive symptoms. These easily recognizable symptoms gave the disease the historical name “madness”. As the disease progresses, negative symptoms, such as social withdrawal and anhedonia, and cognitive symptoms such as dementia become more apparent. Only about one-third of schizophrenic patients can be treated successfully and returned to society, while the remainder is generally institutionalized. The burden on society of this devastating illness and the toll it takes on family members of affected patients make it one of the most costly of all CNS diseases.
Pharmacological treatment for schizophrenia has traditionally involved blockade of the dopamine system, which is thought to be responsible for its positive symptoms. Such treatment, however, ignores the negative and cognitive aspects of the disease. Another neurotransmitter system believed to play a role in schizophrenia is the glutamate system, the major excitatory transmitter system in the brain. This hypothesis is based on the observation that blockade of the glutamate system by compounds such as PCP (“angel dust”) can replicate many of the symptoms of schizophrenia, including its positive, negative, and cognitive aspects. If schizophrenia involves a deficit of glutamatergic transmission, augmentation of the glutamate system, and specifically the NMDA receptor, can be beneficial. While glutamate is the principle agonist at NMDA receptors, glycine is required as a co-agonist to set the “tone” of the receptor for its response to glutamate. Enhancing this “tone” by increasing the effect of glycine would augment NMDA neurotransmission, and provide potential benefit in the treatment of schizophrenia.
A specific mechanism for augmenting the glycinergic “tone” of the NMDA receptor was disclosed recently by Bergeron, et al. (Proc. Natl. Acad. Sci. USA, 95, 15730, (1998)), which is hereby incorporated by reference. This group showed that a specific and potent inhibitor of the glycine type-1 transporter (GlyT1) responsible for removing glycine from the synapse at the NMDA receptor, termed NFPS (WO 97/45115), could enhance NMDA receptor function. For example, NFPS increased the postsynaptic current driven by the NMDA
receptor, an effect blocked by both a specific NMDA-site antagonist and a glycine-site antagonist. Even though glycine levels in the brain are high relative to the amount required to act as an NMDA receptor co-agonist, this work shows that GlyT1 removes glycine efficiently at the synapse, and that inhibition of GlyT1 can augment NMDA receptor function. The present invention provides GlyT1 inhibitors as a treatment for disorders or conditions such as schizophrenia through its augmentation of glutamatergic neurotransmission.